LED driver

Abstract

A LED driver is disclosed herein. In one embodiment, the LED driver comprises a rectifier circuit, a driving current generating circuit, a bus voltage detection circuit, a LED configuration control circuit, and a LED array. The LED driver according to the present disclosure reconfigures the prior LED array, balances usage of each LED by switching operation of each LED, which results in long lifetime of the LED driver while reducing power dissipation or increasing a PF value.

What is claimed is: 
     
       1. A LED driver comprising a rectifier circuit, a driving current generating circuit, a bus voltage detection circuit, a LED configuration control circuit, and a LED array,
 wherein said rectifier circuit has an input for receiving an AC voltage and an output for providing a DC output voltage which is obtained by rectifying said AC voltage; 
 said driving current generating circuit has an input for receiving said DC voltage and an output for providing a driving current to said LED array; 
 said bus voltage detection circuit detects a bus voltage in said driving current generating circuit and has an output for providing a value of said bus voltage; 
 said LED configuration control circuit controls on and off states of LEDs in said LED array in accordance with said value of said bus voltage; and 
 said LED array comprises a plurality of LEDs connected in series with each other and one or more switches each connected in parallel with at least one of said plurality of LEDs, and said LED configuration control circuit controls on and off states of said switches, 
 wherein said driving current generating circuit outputs said driving current which is adjusted in accordance with an actual operation state of each LED in said LED array, 
 said driving current generating circuit divides said bus voltage into a plurality of voltage levels, and divides said driving current into a plurality of current levels, 
 when said bus voltage detection circuit detects that said level of said bus voltage decreases gradually, the number of said LEDs connected in series in an on state decreases gradually, and said driving current increases to corresponding one of said plurality of current levels; 
 when said bus voltage detection circuit detects that said level of said bus voltage increases gradually, said number of said LEDs connected in series in an on state increases gradually, and said driving current decreases to corresponding one of said plurality of current levels. 
 
     
     
       2. The LED driver according to  claim 1 , wherein
 when said bus voltage detection circuit detects that said bus voltage has a first voltage value, said number of said LEDs connected in series in an on state has a minimum value, and said driving current is adjusted to be a first current value; 
 when said bus voltage detection circuit detects that said bus voltage has a second voltage value, said number of said LEDs connected in series in an on state has a value between said minimum value and a maximum value, and said driving current is adjusted to be a second current value; 
 when said bus voltage detection circuit detects that said bus voltage has a third voltage value, said number of said LEDs connected in series in an on state has said maximum value, and said driving current is adjusted to be a third current value. 
 
     
     
       3. The LED driver according to  claim 2 , wherein said LED array comprises said plurality of switches and said plurality of LEDs which are connected to each other, and wherein said plurality of LEDs are connected in series between a high output voltage terminal and a low output voltage terminal of said driving current generating circuit, and said plurality of switches are each connected in parallel with one or more of said plurality of LEDs. 
     
     
       4. The LED driver according to  claim 3 , wherein said LED array comprises two LEDs and two switches,
 said two LEDs comprises a first LED and a second LED, a cathode of said first LED is connected to an anode of said second LED, and an anode of said first LED and a cathode of said second LED are connected to said high voltage output terminal and said low voltage output terminal, respectively; 
 said two switches comprise a first switch and a second switch, said first switch is connected in parallel with said first LED, and said second switch is connected in parallel with said second LED. 
 
     
     
       5. The LED driver according to  claim 4 , wherein said first voltage value is a minimum voltage value, and said third voltage value is a maximum voltage value, and said first current value is a maximum current value below a rated current of said LEDs, and said third current value is a minimum current value which is one half of said first current value,
 when said bus voltage reaches said first voltage value, said LED configuration control circuit turns off said first switch or said second switch, and said driving current generating circuit adjusts said driving current to be said first current value; 
 when said bus voltage reaches said third voltage value, said LED configuration control circuit turns off said first switch and said second switch, and said driving current generating circuit adjusts said driving current to be said third current value. 
 
     
     
       6. The LED driver according to  claim 3 , wherein said LED array comprises three LEDs and two switches,
 said three LEDs comprises a third LED, a fourth LED and a fifth LED, a cathode of said third LED is connected to an anode of said fourth LED, a cathode of said fourth LED is connected to an anode of said fifth LED, and an anode of said third LED and a cathode of said fifth LED are connected to said high voltage output terminal and said low voltage output terminal, respectively; 
 said two switches comprise a third switch and a fourth switch, said third switch is connected in parallel with said third LED, and said fourth switch is connected in parallel with said fourth LED and said fifth LED which are connected in series with each other; or 
 said third switch is connected in parallel with said fifth LED, and said fourth switch is connected in parallel with said third LED and said fourth LED which are connected in series with each other. 
 
     
     
       7. The LED driver according to  claim 6 , wherein said first voltage value is a minimum voltage value, said third voltage value is a maximum voltage value, and said second voltage value is a value between said minimum voltage value and said maximum voltage value, and said first current value is a maximum current value below a rated current of said LEDs, said second current value is a value between a minimum current value and said maximum current value and is one half of said first current value, and said third current value is said minimum current value and is one third of said first current value,
 when said bus voltage reaches said first voltage value, said LED configuration control circuit turns off said third switch and turns on said fourth switch, and said driving current generating circuit adjusts said driving current to be said first current value; 
 when said bus voltage reaches said second voltage value, said LED configuration control circuit turns on said third switch and turns off said fourth switch, and said driving current generating circuit adjusts said driving current to be said second current value; 
 when said bus voltage reaches said third voltage value, said LED configuration control circuit turns off said third switch and said fourth switch, and said driving current generating circuit adjusts said driving current to be said third current value. 
 
     
     
       8. The LED driver according to  claim 3 , wherein said LED array comprises three LEDs and four switches,
 said three LEDs comprises a sixth LED, a seventh LED and an eighth LED, a cathode of said sixth LED is connected to an anode of said seventh LED, a cathode of said seventh LED is connected to an anode of said eighth LED, and an anode of said sixth LED and a cathode of said eighth LED are connected to said high voltage output terminal and said low voltage output terminal, respectively; 
 said four switches comprise a fifth switch, a sixth switch, a seventh switch and an eighth switch, said fifth switch is connected in parallel with said sixth LED, said seventh switch is connected in parallel with said eighth LED, said sixth switch is connected in parallel with said seventh LED and said eighth LED which are connected in series with each other, and said eighth switch is connected in parallel with said sixth LED and said seventh LED which are connected in series with each other. 
 
     
     
       9. The LED driver according to  claim 8 , wherein said seventh switch and said eighth switch maintain an off state, said first voltage value is a minimum voltage value, said third voltage value is a maximum voltage value, and said second voltage value is a value between said minimum voltage value and said maximum voltage value, and said first current value is a maximum current value below a rated current of said LEDs, said second current value is a value between a minimum current value and said maximum current value and is one half of said first current value, and said third current value is said minimum current value and is one third of said first current value,
 when said bus voltage reaches said first voltage value, said LED configuration control circuit turns off said fifth switch and turns on said sixth switch, and said driving current generating circuit adjusts said driving current to be said first current value; 
 when said bus voltage reaches said second voltage value, said LED configuration control circuit turns on said fifth switch and turns off said sixth switch, and said driving current generating circuit adjusts said driving current to be said second current value; 
 when said bus voltage reaches said third voltage value, said LED configuration control circuit turns off said fifth switch and said sixth switch, and said driving current generating circuit adjusts said driving current to be said third current value. 
 
     
     
       10. The LED driver according to  claim 8 , wherein said fifth switch and said sixth switch maintain an off state, said first voltage value is a minimum voltage value, said third voltage value is a maximum voltage value, and said second voltage value is a value between said minimum voltage value and said maximum voltage value, and said first current value is said maximum current value, said second current value is a value between a minimum current value and said maximum current value and is one half of said first current value, and said third current value is said minimum current value and is one third of said first current value,
 when said bus voltage reaches said first voltage value, said LED configuration control circuit turns off said seventh switch and turns on said eighth switch, and said driving current generating circuit adjusts said driving current to be said third current value; 
 when said bus voltage reaches said second voltage value, said LED configuration control circuit turns on said seventh switch and turns off said eighth switch, and said driving current generating circuit adjusts said driving current to be said second current value; 
 when said bus voltage reaches said third voltage value, said LED configuration control circuit turns off said seventh switch and said eighth switch, and said driving current generating circuit adjusts said driving current to be said first current value.